Add S3/MinIO storage backend tests for storage.py

21 test cases covering:
- S3StorageBackend: read, write, exists, path_for with mocked boto3
- Error handling: NoSuchKey exception, generic 404, non-404 re-raise
- Bucket auto-creation on init and graceful handling of creation failure
- Constructor credential/endpoint passthrough
- LocalStorageBackend: round-trip read/write, missing file, empty file
- get_storage_backend() factory: local/s3 selection, case-insensitivity

Closes leeworks-agents/SPARC#1660

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_storage.py

@@ -0,0 +1,263 @@
+"""Tests for S3/MinIO storage backend in storage.py.
+
+Covers issue #1660:
+- S3StorageBackend read, write, exists, path_for
+- Error handling: NoSuchKey, generic S3 errors, bucket auto-creation
+- get_storage_backend() factory function
+- LocalStorageBackend (basic sanity checks)
+"""
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from SPARC.storage import LocalStorageBackend, S3StorageBackend, get_storage_backend
+
+
+# ---------- S3StorageBackend ----------
+
+class TestS3StorageBackend:
+    """Tests for the S3-compatible storage backend."""
+
+    @pytest.fixture
+    def s3_backend(self):
+        """Create an S3StorageBackend with a fully mocked boto3 client."""
+        with patch.dict("sys.modules", {"boto3": MagicMock()}):
+            import boto3 as mock_boto
+            mock_s3 = MagicMock()
+            mock_boto.client.return_value = mock_s3
+            mock_s3.head_bucket.return_value = {}
+
+            backend = S3StorageBackend(
+                bucket="test-bucket",
+                endpoint_url="http://minio:9000",
+                access_key="minioadmin",
+                secret_key="minioadmin",
+            )
+            # Expose mock for assertions
+            backend._mock_s3 = mock_s3
+            yield backend
+
+    def test_write_puts_object(self, s3_backend):
+        """write() calls put_object with correct bucket, key, and body."""
+        s3_backend.write("US-12345678-B2.pdf", b"PDF content here")
+
+        s3_backend._mock_s3.put_object.assert_called_once_with(
+            Bucket="test-bucket",
+            Key="US-12345678-B2.pdf",
+            Body=b"PDF content here",
+            ContentType="application/pdf",
+        )
+
+    def test_read_returns_body(self, s3_backend):
+        """read() returns the Body content from get_object."""
+        mock_body = MagicMock()
+        mock_body.read.return_value = b"PDF data"
+        s3_backend._mock_s3.get_object.return_value = {"Body": mock_body}
+
+        result = s3_backend.read("US-12345678-B2.pdf")
+
+        assert result == b"PDF data"
+        s3_backend._mock_s3.get_object.assert_called_once_with(
+            Bucket="test-bucket",
+            Key="US-12345678-B2.pdf",
+        )
+
+    def test_read_nosuchkey_raises_file_not_found(self, s3_backend):
+        """read() raises FileNotFoundError when object does not exist."""
+        # Create a NoSuchKey exception class on the mock
+        nosuchkey = type("NoSuchKey", (Exception,), {})
+        s3_backend._mock_s3.exceptions.NoSuchKey = nosuchkey
+        s3_backend._mock_s3.get_object.side_effect = nosuchkey("not found")
+
+        # Reassign s3 to trigger the except branch
+        s3_backend.s3 = s3_backend._mock_s3
+
+        with pytest.raises(FileNotFoundError, match="S3 object not found"):
+            s3_backend.read("missing.pdf")
+
+    def test_read_generic_404_raises_file_not_found(self, s3_backend):
+        """read() handles generic 404 errors from S3-compatible APIs."""
+        nosuchkey = type("NoSuchKey", (Exception,), {})
+        s3_backend._mock_s3.exceptions.NoSuchKey = nosuchkey
+        s3_backend.s3 = s3_backend._mock_s3
+        s3_backend.s3.get_object.side_effect = Exception("An error occurred (404)")
+
+        with pytest.raises(FileNotFoundError, match="S3 object not found"):
+            s3_backend.read("missing.pdf")
+
+    def test_read_other_error_re_raises(self, s3_backend):
+        """read() re-raises non-404 errors."""
+        nosuchkey = type("NoSuchKey", (Exception,), {})
+        s3_backend._mock_s3.exceptions.NoSuchKey = nosuchkey
+        s3_backend.s3 = s3_backend._mock_s3
+        s3_backend.s3.get_object.side_effect = Exception("Internal server error")
+
+        with pytest.raises(Exception, match="Internal server error"):
+            s3_backend.read("some-file.pdf")
+
+    def test_exists_returns_true_for_existing_object(self, s3_backend):
+        """exists() returns True when head_object succeeds with content."""
+        s3_backend._mock_s3.head_object.return_value = {"ContentLength": 1024}
+
+        assert s3_backend.exists("US-12345678-B2.pdf") is True
+
+    def test_exists_returns_false_for_missing_object(self, s3_backend):
+        """exists() returns False when head_object raises an exception."""
+        s3_backend._mock_s3.head_object.side_effect = Exception("Not Found")
+
+        assert s3_backend.exists("missing.pdf") is False
+
+    def test_exists_returns_false_for_zero_length(self, s3_backend):
+        """exists() returns False when object has zero content length."""
+        s3_backend._mock_s3.head_object.return_value = {"ContentLength": 0}
+
+        assert s3_backend.exists("empty.pdf") is False
+
+    def test_path_for_returns_s3_uri(self, s3_backend):
+        """path_for() returns an s3:// URI."""
+        path = s3_backend.path_for("US-12345678-B2.pdf")
+
+        assert path == "s3://test-bucket/US-12345678-B2.pdf"
+
+    def test_constructor_creates_bucket_if_missing(self):
+        """Constructor creates the bucket if head_bucket fails."""
+        with patch.dict("sys.modules", {"boto3": MagicMock()}):
+            import boto3 as mock_boto
+            mock_s3 = MagicMock()
+            mock_boto.client.return_value = mock_s3
+            mock_s3.head_bucket.side_effect = Exception("Bucket not found")
+
+            S3StorageBackend(
+                bucket="new-bucket",
+                endpoint_url="http://minio:9000",
+                access_key="admin",
+                secret_key="admin",
+            )
+
+            mock_s3.create_bucket.assert_called_once_with(Bucket="new-bucket")
+
+    def test_constructor_handles_bucket_creation_failure(self):
+        """Constructor logs warning but does not crash if bucket creation fails."""
+        with patch.dict("sys.modules", {"boto3": MagicMock()}):
+            import boto3 as mock_boto
+            mock_s3 = MagicMock()
+            mock_boto.client.return_value = mock_s3
+            mock_s3.head_bucket.side_effect = Exception("Bucket not found")
+            mock_s3.create_bucket.side_effect = Exception("Permission denied")
+
+            # Should not raise
+            backend = S3StorageBackend(
+                bucket="locked-bucket",
+                endpoint_url="http://minio:9000",
+                access_key="admin",
+                secret_key="admin",
+            )
+            assert backend.bucket == "locked-bucket"
+
+    def test_constructor_passes_endpoint_and_credentials(self):
+        """Constructor passes endpoint_url and credentials to boto3.client."""
+        with patch.dict("sys.modules", {"boto3": MagicMock()}):
+            import boto3 as mock_boto
+            mock_s3 = MagicMock()
+            mock_boto.client.return_value = mock_s3
+
+            S3StorageBackend(
+                bucket="test",
+                endpoint_url="http://minio:9000",
+                access_key="mykey",
+                secret_key="mysecret",
+            )
+
+            mock_boto.client.assert_called_with(
+                "s3",
+                endpoint_url="http://minio:9000",
+                aws_access_key_id="mykey",
+                aws_secret_access_key="mysecret",
+            )
+
+
+# ---------- LocalStorageBackend ----------
+
+class TestLocalStorageBackend:
+    """Basic sanity checks for the local filesystem backend."""
+
+    def test_write_and_read(self, tmp_path):
+        """Write and read round-trip produces identical content."""
+        backend = LocalStorageBackend(base_dir=str(tmp_path))
+        backend.write("test.pdf", b"hello world")
+
+        result = backend.read("test.pdf")
+        assert result == b"hello world"
+
+    def test_read_missing_file_raises(self, tmp_path):
+        """Reading a non-existent file raises FileNotFoundError."""
+        backend = LocalStorageBackend(base_dir=str(tmp_path))
+
+        with pytest.raises(FileNotFoundError):
+            backend.read("nonexistent.pdf")
+
+    def test_exists_true_for_written_file(self, tmp_path):
+        """exists() returns True after writing a file."""
+        backend = LocalStorageBackend(base_dir=str(tmp_path))
+        backend.write("test.pdf", b"data")
+
+        assert backend.exists("test.pdf") is True
+
+    def test_exists_false_for_missing_file(self, tmp_path):
+        """exists() returns False for non-existent file."""
+        backend = LocalStorageBackend(base_dir=str(tmp_path))
+
+        assert backend.exists("missing.pdf") is False
+
+    def test_exists_false_for_empty_file(self, tmp_path):
+        """exists() returns False for zero-length file."""
+        backend = LocalStorageBackend(base_dir=str(tmp_path))
+        backend.write("empty.pdf", b"")
+
+        assert backend.exists("empty.pdf") is False
+
+    def test_path_for_returns_full_path(self, tmp_path):
+        """path_for() returns the full filesystem path."""
+        backend = LocalStorageBackend(base_dir=str(tmp_path))
+        path = backend.path_for("test.pdf")
+
+        assert path == str(tmp_path / "test.pdf")
+
+
+# ---------- get_storage_backend() factory ----------
+
+class TestGetStorageBackend:
+    """Tests for the storage backend factory function."""
+
+    @patch("SPARC.storage.config")
+    def test_returns_local_backend_by_default(self, mock_config):
+        """Default config returns LocalStorageBackend."""
+        mock_config.storage_backend = "local"
+
+        backend = get_storage_backend()
+
+        assert isinstance(backend, LocalStorageBackend)
+
+    @patch("SPARC.storage.config")
+    def test_returns_s3_backend_when_configured(self, mock_config):
+        """Setting storage_backend=s3 returns S3StorageBackend."""
+        mock_config.storage_backend = "s3"
+        mock_config.s3_bucket = "test-bucket"
+        mock_config.s3_endpoint_url = "http://minio:9000"
+        mock_config.s3_access_key = "key"
+        mock_config.s3_secret_key = "secret"
+
+        with patch.dict("sys.modules", {"boto3": MagicMock()}):
+            backend = get_storage_backend()
+
+        assert isinstance(backend, S3StorageBackend)
+
+    @patch("SPARC.storage.config")
+    def test_case_insensitive_backend_selection(self, mock_config):
+        """Backend selection is case-insensitive."""
+        mock_config.storage_backend = "LOCAL"
+
+        backend = get_storage_backend()
+
+        assert isinstance(backend, LocalStorageBackend)